Networked sonar observation of selected seabed environments

ABSTRACT

A sonar transducer network for observing a seabed includes a controller. A first transducer assembly includes a first acoustic transducer to convert a first ping to a first electrical signal; and a first transducer processor to receive a first electrical signal from the first acoustic transducer to generate the first transducer data. At least one second transducer assembly is spaced apart from the first transducer assembly. The second transducer assembly includes a second acoustic transducer to convert a second ping to a second electrical signal. The second transducer processor receives the second electrical signal from the second acoustical transducer to generate second transducer data. A network bus communicates first transducer data and second transducer data with the controller.

PRIORITY CLAIM

This application is a continuation of, commonly-owned U.S. Pat. No.8,009,512 issued on Aug. 30, 2011, which is a continuation of U.S. Pat.No. 7,679,995 issued on Mar. 16, 2012, which is a continuation of,commonly-owned U.S. Pat. No. 7,457,196 issued on Nov. 25, 2008 entitled“NETWORKED SONAR OBSERVATION OF SELECTED SEABED ENVIRONMENTS”, which isfully incorporated herein.

FIELD OF THE INVENTION

This invention relates generally to sonar and, more specifically, tocollecting and compiling return data from networked sonar transducerassemblies.

BACKGROUND OF THE INVENTION

Whales, seals, sea lions, catadromous fish such as eels and anadromousfish such as shad and salmon all migrate through confined waterways suchas Puget Sound or Alaska's Inside Passage. The main means of determiningpopulations and movement have been through spotting, i.e. humanobservers at chokepoints. Chokepoints have been traditionally atpassages through which the migrating population must pass. Where thepassages have been synthetic and narrow, such as fish ladders, or atnatural constrictions, such as the mouths of streams, the movement ofthe migratory population has been readily estimated by visual sighting.Generally, the narrower the constriction, the better the count.

Only anadromous fish, however, migrate into narrow streams where suchcounts are facilitated by constrictions in the migratory waterway.Cetacean species rarely enter freshwater streams and will not readily becounted in such confined waterways. Yet the whales do pass through somewell-defined passages on their migratory routes.

Orca whales, for example, can be observed to move between Puget Sound inWashington, through the Strait of Georgia in British Columbia, then onto southeastern Alaska; traveling through Prince William Sound to thewaters around Kodiak Island. Given the breadth of any of several inlandpassages, visual counting lacks a great deal of the certainty necessaryto accurately gauge the extent of the Orca population as they migrate.

Complicating the count is the fact that within the same waters,Humpback, Grey and other cetacean species live and move. Discernment ofone whale species from another in the same space is also necessary foraccurately assessing the population. All of these species regularly passthrough the same defined chokepoints in the inland waterways. Becausewhale movement is predictable and includes swimming through predictedpassages, accurate counts could be obtained by monitoring the seabedenvironment at each of these chokepoints to discern passage.

Selected sonar frequencies have been found to detect whales withoutimparting injury to the whale's own sonar guidance system. Sonar,however, only propagates in a cone defining a solid angle. Countingschemes to date have placed the sonar across the mouth of a chokepoint.Very few chokepoints, however, can be effectively monitored bypositioning a single solid angle cone, for doing so requires theassumption that the whales will pass in single file through thechokepoints. Ganging sonar installations has been one strategy forenhancing the accuracy of counting results by placing severaltransducers along the migration path and comparing results to come upwith counts that are in good agreement. A second ganging strategyconsists of filing a chokepoint with several transducer cones, stackedto completely and non-overlappingly fill the chokepoint, but suchganging suffers from a lack of coordination of results such that asingle whale might be counted more than once by passing through each ofseveral sonar cones. Additionally, finding such chokepoint spaces thatare readily filled with such transducer cones is difficult.

What is needed, then, is a predictable means of monitoring definedchokepoints with coordinated sonar installations. Comprehensivemonitoring of chokepoints in defined seabed environments facilitatescounting by allowing in-depth observation of all movement within thoseseabed environments.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred and alternative embodiments of the present invention aredescribed in detail below with reference to the following drawings.

FIG. 1 is a perspective view of a transducer assembly;

FIG. 2 a is a perspective view of a networked sonar array with a singletransducer assembly in networked communication;

FIG. 2 b is a block diagram of the networked sonar array with the singletransducer assembly;

FIG. 3 is a detailed block diagram of the networked sonar array with thesingle transducer assembly;

FIG. 4 a is a seabed environment including surf zone bathymetry factors;

FIG. 4 b is a seabed environment with the seawater removed to revealsurf zone bathymetry factors;

FIG. 4 c is a detail of two rocks within the seabed environment;

FIG. 5 is a flow chart of analysis of the suppression algorithm;

FIG. 6 is a perspective view of a seabed environment with a networkedsonar array in situ;

FIG. 7 is a plan view of a constricted seabed volume between piers; and

FIG. 8 is a perspective view of the seabed volume between piers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

By way of overview, a sonar transducer network for observing a seabedincludes a controller. A first transducer assembly includes a firstacoustic transducer to convert a first ping to a first electricalsignal; and a first transducer processor to receive a first electricalsignal from the first acoustic transducer to generate the firsttransducer data. At least one second transducer assembly is spaced apartfrom the first transducer assembly. The second transducer assemblyincludes a second acoustic transducer to convert a second ping to asecond electrical signal. The second transducer processor receives thesecond electrical signal from the second acoustical transducer togenerate second transducer data. A network bus communicates firsttransducer data and second transducer data with the controller.

Networked Transducer Assemblies with Two-Axis Mounts

FIG. 1 illustrates a non-limiting example of a transducer assembly 10including a transducer electronics subassembly 12. The transducerelectronics subassembly 12 includes a transducer processor (not shown)and a transducer (not shown) also referred to as transducer ceramics(referring to the fact that transducers commonly include piezoelectricceramic transducers).

The transducer electronics subassembly 12 is mounted on a two-axis mount15. The two-axis mount 15 serves as a platform not only for thetransducer electronics subassembly 12 but also for such environmentalsensors 18. By way of non-limiting example, environmental sensorsinclude those which measure environmental conditions such astemperature, salinity, and relative pressure.

Sound speed is slower in fresh water than in sea water. In all watersound velocity is affected by density (or the mass per unit of volume).Density is affected by temperature, dissolved molecules (usuallysalinity), and pressure. The speed of sound (in feet per second) isapproximately equal to 4388+(11.25×temperature (in ° F.))+(0.0182×depth(in feet)+salinity (in parts-per-thousand)). This empirically derivedapproximation equation is reasonably accurate for normal temperatures,concentrations of salinity and the range of most ocean depths.

Ocean temperature varies with depth, but at between 30 and 100 metersthere is often a marked change, called a thermocline, dividing thewarmer surface water from the cold, still waters that make up the restof the ocean. The presence of the thermocline can frustrate sonar, for asound originating on one side of the thermocline tends to be bent, orrefracted, off the thermocline. The thermocline may be present inshallower coastal waters; however, wave action will often mix the watercolumn and eliminate the thermocline. Water pressure also affects soundpropagation. Increased pressure increases the density of the water andraises the sound velocity. Increases in sound velocity cause the soundwaves to refract away from the area of higher velocity. The mathematicalmodel of refraction is called Snell's law. For these reasons, monitoringof ambient water temperature, salinity, and relative pressure optionallyallows normalization of the speed of sound through the ambient water,thereby giving more precise ranging.

The Remote Ocean Systems™ two-axis pan and tilt mounts are onenon-limiting example of a suitable two-axis mount. By way of furthernon-limiting example, a two-axis mount will include actuators for eachaxis including either of a reversible synchronous motor or a brushlessstepper motor coupled to low backlash harmonic gearing. Optionally,rugged design of the gear train allows stalling of either output shaftwithout damage to the gears or the motors.

The two-axis mount is, optionally, equipped with internal limit switchesand position feedback potentiometers on both axes. The potentiometerssense pan and tilt orientation angles for providing azimuth anddepression angles (or “pan and tilt” angles) and present thatinformation to the transducer processor (not shown) for inclusion intransducer data.

In the pictured embodiment of the two-axis mount 15 of the transducerassembly 10, a mounting flange 21 provides an advantageous means ofaffixing the two-axis mount 15 to a stationary hard point from which tooperate.

Referring to FIG. 2 a, an embodiment of a networked sonar transducerarray 7 includes a transducer electronics subassembly 12,communicatively connected to a controller 27 by means of a network bus24, in this case a waterproof Ethernet cable, through a network bus 24including a fiber optic cable with suitable nodes or other such networkmeans.

In a non-limiting exemplary embodiment, the communication between thecontroller 27 and any of at least one transducer electronics subassembly12 is by means of addressing of packets from a sending node to areceiving node. In this application, the term Ethernet is used toreference all of the IEEE 802 LAN protocols, including but not limitedto Token, FDDI, and ATM but because Ethernet has some common featureswith networking standards that are not part of the IEEE 802.3 Ethernetstandard, but support the Ethernet frame format, and are capable ofinteroperating with it, the term Ethernet, as used herein any networkover any bus such as a twisted pair; coaxial; fiber optic conduits; waveguides; or wireless networks such as WiFi or Bluetooth, or, importantly,any combination of the busses.

Addressing of packets is handled on Ethernet, as on all IEEE 802 LANs,by giving each peer a unique 48-bit MAC address. Network adaptersnormally do not pass packets intended for other Ethernet cards to thehost to improve performance but can also be placed in promiscuous modewhere they pass every packet to the host. Adapters generally comeprogrammed with a globally unique address but this can be overriddeneither to avoid an address change when an adapter is replaced or to uselocally administrated addresses. The network bus 24 may be any networkbus capable of supporting a LAN including the transducer electronicsassembly 12.

By way of further explanation of the basic networked sonar transducerarray 7, reference to FIG. 2 a shows a block diagram of the network bus24 including transducer interface cards 33, 36 and a controllerinterface card 51 shown in FIG. 2 b. Representing the same elementsshown in the perspective view that is FIG. 1, the embodiment of thenetworked sonar transducer array 7 includes the transducer electronicssubassembly 12, communicatively connected to the controller 27 by meansof the network bus 24. Additionally, the controller 27 manages thenetwork bus 24 including assignment of the resources on the network bymeans of dynamic host configuration protocol (DHCP). DHCP is an Internetprotocol for automating the configuration of computers that communicateusing the TCP/IP protocol. DHCP can be used to assign IP addresses, todeliver TCP/IP stack configuration parameters such as the subnet maskand default router. DHCP transmits other configuration information toeach of the components on a network and assigns addresses for thecontroller 27 and the several transducer interface cards 33, 36.

Network management is set forth in a non-limiting embodiment by a serversection of the controller 27 called a network controller 45. By way ofnon-limiting example, a network controller 45 includes a processorconfigured to manage the network traffic without requiring dedication ofhost CPU cycles. The network controller 45 facilitates networkedcommunication by processing TCP/IP communications. Using an autonomousnetwork controller 45 prevents formation of a bottleneck within thecontroller 27.

The network controller 45 operates responding to instructions within anoperating system stored in machine-readable form on the non-volatilememory 42. By way of non-limiting example, the non-volatile memory in anembodiment is identified as a chipDISK™, a fully IDE-compatible flashhard disk designed to replace the customary hard disk. The chipDISK™ isan example of a flash memory technology selected to ruggedize thecontroller 27 for use outside of a laboratory environment.Advantageously, flash memory is insensitive to tremors, vibrations,impacts, fluctuations in temperature and magnetic fields. Flash memoryis, therefore, well-suited for use in mobile equipment and systems whichneed to withstand severe influences. Additionally, having a very smallform factor, the flash memory allows the configuration of a more compactand therefore portable controller 27.

The remaining infrastructure necessary to support the controller networkincludes a transmitter card 51, along with a power amplifier board 48,and the power supply section 54. The power supply section 54 feeds thenetwork controller 45, the power amplifier board 48, the transmittercard 51, and the non-volatile memory 52. The power supply board 54feeding a logical power supply 5-volt regulator 57 provides power forlogical switching circuits. In the non-limiting embodiment, thedescribed elements of the controller 27 function as the principal serverin the networked sonar transducer array 7.

At least one transducer electronics subassembly 12 is in networkedcommunication with the controller 27. The transducer electronicssubassembly 12 includes a transducer processor 30, itself including, byway of non-limiting example, network transmission 33 and receptionboards 36 to enable communication through the network bus 24, as well asa transducer 39. The transducer processor 30 is further configured todrive a transducer 39 and to process the signals from the transducer 39to create transducer data to be fed over the network bus 24 to thecontroller 27. In one embodiment, the controller 27 time stampstransducer data and concatenates the time stamped transducer data withdata including azimuth angle and angle of depression data.

The transducer 39 generates and receives sonar energy by means ofpiezoelectric ceramics. A variety of piezoelectric ceramics may besuitable for the fabrication of the transducer 39. Often ceramicformulations are chosen to optimize a “Q factor,” a term used todescribe a measure of “quality” of a resonant system. Resonant systemsrespond to frequencies close to their natural frequency much morestrongly than to other frequencies. Systems with a high Q factorresonate with greater amplitude at the resonant frequencies than systemswith a low Q factor. Enhancing the Q factor of the ceramic assures thatreception of sonic energy within the band used for ranging will make thetransducer both more sensitive and more discerning. A lower Q factorallows the piezoelectric ceramic transducer makes the transducerresponsive to a wider range of frequencies. In some embodiments lower Qfactors will facilitate a desired response, in others, a higher Q allowsfor dedicated use at a particular frequency. Alternatively, where aplurality of frequencies is desired, the single transducer electronicssubassembly 12 may, optionally, contain multiple transmitters andreceivers for each receiver transmitter pair being configured to operateat different frequencies.

Transducers 39 can operate as both transmitters and receivers, or theycan be configured to be either solely transmitters or solely receiversdepending upon electronics supporting the piezoelectric ceramic. Where asonar installation includes a distinct transmitter and a distinctreceiver, a shared timing signal is necessary to measure transit timefor a ping traveling between the transmitter and receiver through amedium such as seawater. Time stamping pings at the receiver aftergenerating pings at known times provides a calculable transit time.

One advantage of a networked sonar transducer array 7 is that eachcomponent of the transducer array operates with access to a network timesignal that, advantageously can also be used to time components of thesonar transducer array 7. That network time signal can be used to clockacoustical emissions and receptions at distinct transducers 39, allowingoperation analogous to that of bistatic radar. In bistatic operation, asingle emitter transducer 39 can ping a plurality of targets within themonitored seabed environments 101 and the ping can be reflected andsubsequently received at a number of distinct directional receivertransducers 39.

Piezoelectric ceramics exploited as transducers 39 may be optionallyconfigured for specific transmission or reception tasks. For instance,where a desired function of a one of the networked transducers 39 is toserve as a “trip wire,” the piezoelectric ceramic might be configured tobe horizontally omnidirectional, i.e. having a beam pattern that isvirtually equal in all horizontal directions. By transmitting a singleping that is, in turn, heard by a number of placed receivers, changes ina seabed environment 101 may be noted and localized. In that fashion,detection of movement within the broad scope monitored by the severalreceiving transducers can serve to initiate further probing action. Thecontroller 27, in response to the detected movement, directs thedistinct transducer assemblies 12 to derive further information from thearea in the seabed environment 101 where the movement was detected.

The ability to craft distinct configurations of piezoelectric ceramicsis particularly exploitable in the context of networked sonar transducerarray 7. By selectively fabricating transducers 39 for distinctcapabilities and configuring the placement of the transducers within amonitored submarine environment 101 to exploit the selectedcharacteristics of the fabricated transducers 39, coverage of the seabedmay be tailored for optimal detection of change within the seabedenvironment 101. A networked sonar transducer array 7 may includenarrow-beam, split-beam, side-scan and wide-beam transducers selectedfor the particular assignment within the seabed environment 101. Forinstance, sidescan transducers 39 are designed for a focused directionalbeam pattern to the side and may be advantageously exploited to monitorelongate margins of the designated seabed environment 101.

In a further embodiment, several transducers 39 are ganged as an arraywithin a single transducer electronics assembly 12, allowing thetransducer processor 30 to switchably address any one of the severaltransducers 39 arranged together as a system. By doing so, thetransducer electronic subassembly 12, as a system, can change its focuson the seabed as the controller 27 dictates. An analogous situation ispresented by the user of bi- or tri-focal glasses. As needed to observean object of interest, the user selects the lens that will yield themost information to the user, generally by casting the eyes to seethrough the selected lens.

Similarly, the single transducer electronics subassembly 12 can beselectively configured to activate distinct piezoelectric ceramics 39without physical replacement but rather by switching that selectivelyincludes one or another piezoelectric ceramic 39, according to the sonarconfiguration designed for the seabed, thereby removing the expenseassociated with placement of multiply and distinctly packagedelectronics subassemblies 12 for each intended focus. In suchnon-limiting exemplary embodiments, the transducer processor 30 isselected to include the ability to switch between the severaltransducers 39 according to direction from the controller 27.

As explained above, the transducer electronics subassembly 12 mayadvantageously communicate between the controller and the severaldistinct transducers by means of one or several network interface cards33, 36. As earlier indicated in the discussion of FIG. 1, a secondnetwork interface card optionally might be dedicated to receivinginformation from the environmental condition sensor 18 (FIG. 1) andconveying it from the transducer processor 30 to the controller 27, inone of several embodiments. Alternately, the transducer processor 30 mayperform normalization of the received echo timings based upon observedenvironmental conditions.

Referring now to FIG. 3, the networked sonar transducer array 7 is shownto include the several data and signal processing capabilities necessaryto more fully exploit the data gathering capabilities of the networkedsonar transducer array 7. It should be noted that for the sake ofdiscussion, the dual functions of the controller 27 and a number ofphysical elements it comprises are duplicated in FIG. 3. This alternateembodiment does not require distinct elements but rather illustratesthat the function of providing 5 volt regulation might be handled by asingle 5 volt regulator even though two distinct 5 volt regulators 57,81 are shown in the diagram. Similarly, the network bus 24 and a rotatorcable 24 a; the hard disk 60, 87; the non-volatile memory 42, 90; andthe processor 45, 84 are each shown as distinct elements but any or allof them may, in the prudent practice of the invention, be embodied by asingle physical unit.

The heart of the controller 27 is the processor 84. The processorreceives data from a plurality of the transducer electronicssubassemblies 12 and sorts the data to give a comprehensive picture ofthe monitored seabed. The processor 84 tasks each of the transducerelectronics subassemblies 12 to specifically monitor an assigned sectoraccording to instructions transmitted to the assembly through thetransmitter board 51 over the network bus 24 to the receiver networkinterface board 36 to selectably select a transducer 39 to specificallyobserve regions within the seabed. The Ethernet switch 75 suitablycorrelates data according to its source in order to facilitate addressedcommunication within the network 24, identifying both the source and thedestination of data. Data generally streams to the processor 84 from thetransducers 39 and commands flow down to the transducers 39. By suchmeans, the identify data is associated with its source transducerelectronics subassembly 12.

In an alternate embodiment, instructions for the processor 84 reside ina machine readable form on the non-volatile memory 90. The processor 84receives the data from the transducer 39 and builds a picture in abuffer corresponding to the transducer 39 on the hard drive 87. To theextent necessary to observe a particular region based upon anorientation of the two-axis mount 15 (FIG. 1), the processor 84generates instructions to suitably orient the transducer 39 relative tothe mount 15. The processor 84 generates drive instructions and sendsthem through the motor control 69 down the rotator cable 24 a. The driveinstructions are received within the transducer electronics subassembly12 at the dual axis rotator 63. The dual axis rotator 63 suitablyactivate the mount 15 and its attendant actuators to orient thetransducer 39 while the potentiometers (not shown) sense pan and tiltorientation angles. The azimuth and depression angles that the dual axisrotator 63 communicates back to the processor 84 then confirm thealignment of the transducer 39.

The processor 84 populates the several buffers on the hard disk 87 toproduce complete pictures of the monitored seabed from each of theplurality of transducer electronics subassemblies 12. The processor 84further compares the data received to determine if some aspect of thedata matches any of a number of alarm states recorded in theinstructions stored in machine readable form on the non-volatile memory90. If the data matches one of the alarm state, the processor 84 feedssuitable instructions to the relay unit 93 which suitably activateseither or both of a strobe 99 or a speaker 96 with an annunciatedwarning according to the particular alarm state.

Benchmarks in Seabed

Advantageously, in most instances where a submarine environment 101 isto be monitored, detailed bathymetric data exists to reveal the contourand significant features of the submarine landscape. From a vessel, rawsonar data is collected using the sonar sensors. To calculate theprecise position of the vessel, a computer constantly monitors thevessel's position according to a GPS system. Heave, pitch and roll datafrom the vessel's motion sensor and tide information from the tide gaugeare input to condition and normalize the data. The large quantities ofdata returned from the site survey (typically hundreds of megabytes) areprocessed to provide a high resolution digital terrain map (DTM) with atypical positional resolution of 5-10 centimeters and a depth resolutionof 1 centimeter in one non-limiting example. The DTMs are rendered usingseabed visualization software.

Sonar technology is not the only method of gathering seabed topography.Underwater photography or video can provide the most detailed view ofthe seafloor. However, the cameras are limited to short distances as theartificial light does not penetrate the seawater effectively. In somecases visibility is degraded due to disturbed sediment and otherenvironmental factors. Cameras placed on a remotely operated vehicle(ROV) can be used to gather data to augment the data resulting fromrendering.

Satellite technology is another method that can be used to map theseafloor since, due to gravity, the shape of the sea surface is closelyrelated to that of the seafloor. The depth of the ocean can vary byapproximately 200 meters solely from the gravitational pull of largeunderwater seamounds such as an underwater volcano. Conversely, theocean surface can downwarp over seabed trenches. Satellites measure thetime it takes to bounce radio waves off the surface of the ocean andtherefore calculate the height of the sea surface. Ocean topographyusing satellites can provide a global view of the ocean floor butgenerally lack the precision provided by sonar. When the several datacollection methods are used in conjunction, one with the others, a veryaccurate rendering of the seabed is derived from the surface elevations.

Based upon an accurate and detailed view of the seabed, a networkedsonar transducer array is designed to sense the seabed and the submarineenvironment 101 above the seabed. Referring to FIG. 4 a, the surf zoneseabed 101 a is portrayed with seawater present and as having severalnotable shoreline features, such as a groin 102, opposing jetties 105and 108 and a pier 112. Not themselves seabed features, these marinefeatures are indicative of corresponding submarine features that willmake up the fixed seabed.

Referring to FIG. 4 b, the bathymetric features such as the sandbars 102a encompassing the groin 102, the footings 105 a of the jetty 105, andthe pilings 112 a, 112 b, and 112 c become evident, as do other featuressuch as canyon rocks 114, 117. These submarine features representirregularities in the seabed; they are fixed, and observation of theseabed by sonar means will repeatedly produce echoes indicative of thesefixed features of the seabed. Once known, display or analysis of thesefeatures is redundant and uninteresting for purposes of monitoring theseabed environment 101, but are extremely important in a process ofplacing transducer assemblies 10 (FIG. 1) in the networked sonartransducer array 7 (FIG. 2 a) within the seabed environment 101.

Given the fixed nature of the several submarine features, the dataobtained by the sonar survey is used to establish a baseline of ambientnoise and reverberation, and fixed and assumed uninteresting physicaltargets, which may be present in the field of view. The processor 84 isprogrammed to “map” these features into memory. Any number of featuresare mapped into memory given their fixed and repeatable nature. Examplesof these features include pilings, ship hulls, sea walls, aquaticvegetation and the seafloor itself.

Once the submarine terrain is known and the features isolated, thetransducer assemblies 10 (FIG. 1) of the networked sonar transducerarray 7 (FIG. 2 a) are placed within the submarine environment 101. Asindicated above, a transducer emits in a solid angle cone. Efficientlypacking the submarine environment 101 with solid angle cones is readilyaccomplished by space packing algorithms and aided by the criteria thatoverlap of cones allow placement of the transducers 39 (FIG. 2 b) tosuitably overlap downrange. Due consideration is taken of placement ofsensor to assure visualization of each of the features within the seabedenvironment 101. For instance, the seabed terrain includes two canyonrocks 114, 117. As the rocks 114 and 117 rest within a seabed canyon,placement of the transducer 39 (FIG. 2 b) will duly exploit alignment ofthe cone with the canyon to allow a clear “view” of the canyon rocks114, 117 from the selected transducer site (not shown).

Once transducers 39 (FIG. 2 b) are placed, the background collectionphase begins with a scan of the seabed environment 101. Scanningincludes “pinging” or generating “pings” which are short pulses of soundenergy generated to propagate from the transducer 39 (FIG. 2 b) throughthe submarine seabed environment 101 and used for ranging. Scanning ispinging while the transducer 39 (FIG. 2 b) resides in a variety oforientations to build a composite of the submarine seabed environment101 as the transducer 39 receives reflected pings.

When the networked sonar transducer array 7 performs the scan of aparticular sector of seabed environment 101 the two-axis mount 15(FIG. 1) drives each transducer to many different orientations duringthe course of the scan. Additionally, transducers 39 are optionallyplaced within the seabed environment 101 in a configuration to assurethat each feature in the seabed environment 101 is viewed by at leastone transducer 39. At any particular orientation, an emitted ping willencounter certain static structures present in the environment 101, forexample, pilings or the bottom. The background collection phase consistsof collecting acoustic data while scanning the transducer through theentire path of the scan. Ideally, the background collection phase is runlong enough for several pings to be collected for each bin oforientations (for example, each 1-degree cone). The size of theorientation bins is configurable by the user.

Bistatic imaging may also optionally be used in a similar fashion togenerate further data as to the nature of the seabed environment 101.Bistatic imaging is a technique for using two transducers 39 (FIG. 2 b)to map a surface, with one emitting and one receiving. The bistaticimaging yields a more detailed image than would have been rendered withjust the transducer 39 (FIG. 2 b). Bistatic imaging can be useful indifferentiating between different sonary surfaces, due to the differentways that sound reflects off of these objects (transducers detect“volume scattering” from less solid surfaces). Additionally, bistaticimaging allows for monitoring spaces between two transducers 39 (FIG. 2b).

Epipolar geometry is the intrinsic projective geometry between twoviews. Resolution of the spatial relations between selected points isindependent of scene structure, and only depends on the transducers' 39(FIG. 2 b) internal parameters and relative pose. The epipolar geometrybetween two views is essentially the geometry of the intersection of theimage planes with the pencil of planes having the baseline as axis (thebaseline is the line joining the transducers 39 (FIG. 2 b) centers).Resolving spatial relations is based upon epipolar geometry to assist inthe search for corresponding points in stereo matching.

At the end of the background collection process, the pings in eachorientation bin are averaged to get a representation of the staticstructure encountered by the acoustic beam when it is in thatorientation. The scan can suitably be correlated with the results of theinitial sonar survey of the seabed environment 101.

Referring to FIG. 4 c, the hard features in the seabed environment 101such as the canyon rocks 114, 117. Such known submarine terrain featuresare compared to the timings of the received pings in order to solve fora transform from one mapping by one transducer 39 (FIG. 2 b) to thenext. Kalman filtering is optionally used to solve for such atransformation relative to the monitored seabed environment 101. Becausethe solution of the transformation need not be done in “real time”iterative processing of the Kalman filter can be used until thespherical coordinates generated at a first transducer 39 (FIG. 2 b) ofreturned pings from its surrounding environment 101 can be used torelate the returns from the first transducer 39 (FIG. 2 b) to those of asecond transducer 39 (FIG. 2 b). Once a solution is derived between eachof the transducers 39 (FIG. 2 b) and each of the remaining transducers39 (FIG. 2 b), the whole of the seabed environment 101 can be describedin spherical coordinates from at least one, but generally twotransducers 39 (FIG. 2 b) in the seabed environment 101.

Spatial Model

Once the whole of the seabed environment 101 is mapped relative to eachof the transducers 39 (FIG. 2 b), monitoring of the seabed environment101 is more readily achieved. The seabed features that are static,having already been used to solve for the suitably transforms betweenthe coordinates as “viewed” from each of the transducers 39 (FIG. 2 b),now become the boundaries of relevant returns. For purposes ofmonitoring the environment 101, no reason exists to expend computerresources for resolving range bins outside of the boundaries defined bythe static features. The boundaries of relevant returns are then mappedto form a by-pass map uses for suppression selection.

Referring to FIG. 5, a filtering method 200 includes examining eachrange bin for suppression according the by-pass map. Commencing at ablock 201, the method continues to determine if the range bin isspatially located within an area where suppression is advantageous at ablock 204. Most of the range of any of the transducers 39 (FIG. 2 b)includes monitorable space; indeed, the placement of the transducers 39(FIG. 2 b) was based upon optimizing the portion of the seabed environseach of the transducers 39 (FIG. 2 b) could monitor. In some instances,activity with a region is known and not considered advantageous tomonitor. By way of non-limiting example, when a vessel passes through anarea being monitored for cetacean activity, the vessel is know an inorder to well track what activity exists around the vessel, suppressionof returns from the vessel prevents those returns from overwhelming theother information discernible in proximity to the vessel. Because thevessel would not be on the by-pass map, it not being a static feature ofthe seabed environs, an option allowing the operator to suppress thereturns at the vessel is useful.

If the range bins are outside of the operator defined area for ad hocsuppression, the method proceeds checking if the range bin is oneidentified by the by-pass map for suppression at a block 207. If not,the range bin is stored unaltered in the buffer at a block 213 and at ablock 297, the analysis proceeds to the next range bin in question.

If, at the block 207 the range bin is found on the by-pass map, at ablock 210, the returns in the range bin are suppressed according to thefilter information stored in the by-pass map. Once the returns aresuitably suppressed, the returns are stored in the buffer, and at theblock 297, the analysis proceeds to the next range bin in question.

Where there are no objects that require operator selected localsuppression, an operator will select a setting of “0” meaning “no localsuppression is requested” and thus, at a block 216, the methoddetermines that no suppression is requested and the method, at a block219, stores the unaltered range bin in the buffer and then at the block297, moves to the next range bin.

If, on the other hand, the operator has selected either of settings “1”or “2” meaning that either of “selective suppression” “suppressionaccording to suppression map,” respectively, are selected, at the block216, the method moves to determine suitable suppression.

A word about the suppression map is appropriate. In this non-limitingexample, the suppression map is a map of filter values selected basedupon the seabed terrain and the operator's “tuning” of results toachieve appropriate sensitivity throughout the range. The suppressionmap is a result of the operator's experience and not based uponautonomous responses of the system.

In the selective suppression mode or operator selected “1” mode, theby-pass map and the suppression map are selectable but deference isgiven to the by-pass map. If the operator selected is detected at ablock 222, the method queries the by-pass map to determine if a by-passfiltering value is associated with the location of the range-bin underanalysis, at a block 225. If no by-pass map entry exists, at a block231, the range bin value is stored in the buffer and at the block 297,the analysis moves to the next range bin.

If a value exists on the by-pass map associated with the spatiallocation of the range bin, the value is suppressed according at a block228 and stored in the buffer. Then, the method moves to the next rangebin for analysis at the block 297.

Where the operator has selected mode “2” only the suppression map isapplied to the range bin returns. Thus, at a block 234, the selection ofmode “2” is verified. At a block 237, the suppression stored inassociation with the range bin spatial location is applied to the rangebin return and at the block 297, the analysis moves to the next rangebin.

Non-Limiting Example of Use of the Networked Sonar Transducer Array

Referring to FIG. 6, an example drawn from a test of the system isilluminating. In an underwater environment 101 a number of existing hardtargets such as canyon rocks 114, 117 exist as part of the staticmembers of the environment 101. For the purposes of this non-limitingexample, these are presumed to be already mapped relative to each of theseveral (in this exemplary case, three) transducer subassemblies 12 a,12 b, 12 c on their respective two-axis mounts 15 a, 15 b, 15 cconfigured as a network of transducer subassemblies 12. In thisnon-limiting example, each of the transducer assemblies have anarrow-angle cone 123 a, 123 b, and 123 c systematically scanning adefined azimuth 126 a, 126 b, 126 c, and for surveillance of theunderwater environment 101. In response to commands generated eitherautonomously or sent to the transducer assembly network 12 for anindividual transducer assembly, 12 b for example, from the controller27, the transducer assemblies may switchably select scanning the azimuth126 in a systematic pattern or training narrow-angle cones 123 forsurveillance of designated point in the underwater environment 101.

Presumed in this example is that the whole of the underwater environment101 is suitably mapped by the above-described methods relative to eachof the transducer subassemblies 12 a, 12 b, 12 c and by means ofepipolar geometry all of the spatial relationships between the terrainincluding hard targets within the underwater environment 101 have beensuitably related to each of the transducer assemblies 12 a, 12 b, 12 cto generate a three-dimensioned buffer representing the space.

As the networked sonar transducer array 7 monitors the underwaterenvironment 101 for movement within the underwater environment 101, allechoes that would emanate from the known static elements such as thecanyon rocks 114, 117 are, in at least one embodiment, suppressed fromanalysis or, optionally, from a graphic display of the space generatedfor operators, as these static elements are known not to be migratingfish or other targets 99 of interest within the environment 101. Thus,where some dynamic element within the environment 101, initiates amovement that is detectable by at least one of the arrayed transducerassemblies 12 a, 12 b, 12 c, that movement may be tracked relativelyeasily independently of the echoes emanating from known static elementswithin the environment 101.

In at least one embodiment, alarming based upon movement within theenvironment 101 is considered to be very useful. For instance, where theselected underwater environment 101 is at a choke-point in a migratorypattern, and where the sort of echoes that might be returned fromdynamic elements in the space are known by certain characteristics,movement of such dynamic elements may, itself, be an event of note,signaling, for example, the return of such a long migratory as an Orcato a territorial water. If “enough” such echoes are received at thetransducer assemblies 12 (based on a user-configurable sensitivityparameter), then an alarm condition is signaled. The actual signalingmay be designated to take the form of triggering relays connected toalarm devices such as a siren or a strobe light, or it may includesending out information over a second network (distinct from the arrayedtransducer assemblies 12) about the position of the dynamic element.Optionally, alarming includes generating a displayed icon at a positioncorrelating with the position of the dynamic element within theenvironment 101. Such an icon might be placed in a three-dimensionedrepresentation of the environment 101 or in the more traditional planposition indicator (PPI) display used in radar applications.

To test the efficacy of the networked sonar transducer array 7, targetsare introduced into the underwater environment 101. One exemplarytarget, a diver 99 a presents a minimal profile to the transducerassembly 12 c as the diver 99 a swims within the wide-angle cone 126 c.Alerted to the changing state within the ambit of the wide-angle cone126 c, either autonomously or at the command of the controller 27, thetransducer assembly 12 c switches from systematically scanning theazimuth 126 c to training the narrow-angle cone 123 c to enableexamining the diver 99 a with the greater discernment that repeatedpinging with the narrow-angle cone 123 c provides. Optionally, thecontroller 27, may order the adjacent transducer assembly 12 b to pivoton its two-axis mount 15 b to further examine the diver 99 a. Generallythe narrow-angle cone 123 b can be trained on the diver 99 a given theepipolar geometric solution already solved for the whole of theunderwater environment 101. Advantageously, the diver 99 a cannotpresent the minimal cross-section to both transducer assemblies 12 b, 12c. For this reason, probability of discernment of the diver 99 a as atarget of interest is greatly enhanced by the simultaneous sensing ofthe diver by the distinct transducer assemblies 12 b, 12 c.

In a second instance, the same non-limiting example of the transducerassembly network 12 includes a diver 99 b using a diver propulsionvehicle such as a tow behind scooter. Diver propulsion vehicles are usedin testing to give distinct velocities and movement to the target.Similarly, the response from the system by way of non-limiting exampleis the same, except to the extent that the transducer assembly 12 b isimplicated as monitoring the test area within the underwater environment101. As a distinct example, the transducer assembly 12 b switches fromscanning the azimuth 126 b to training the narrow-angle cone 123 on thediver 99 b to track the diver 99 b, while the adjacent transducers 12 aand 12 c pivot on their respective mounts 15 a, 15 c to expand theirrespective azimuths 126 a, 126 c to include portions of the azimuth 126b that had been monitored by transducer assembly 12 b therebymaintaining suitable surveillance of a perimeter of the underwaterenvironment 101.

Having the transducer assemblies 12 a, 12 b, and 12 c, each themselvesbeing trainable in response to the controller 27, the networked sonararray 7 can suitably study any movement of a dynamic element within theunderwater environment 101. Another non-limiting example of a responseto movement of dynamic elements with the underwater environment 101 ispresented by the presence of a school of fish 99 c within the underwaterenvironment 101.

Movement of fish 99 c through an underwater environment 101 is generallyby known means. Fish will travel at known velocities, school ingenerally known fashions, and present a reflectivity to sonar that canbe predicted. From species to species, these parameters may vary, butwithin a known species, study and cataloging will allow classificationof schools of fish or other marine life according to its species andnumber. Doing so, however, will not be the result of one or two “pings”from a transducer assembly 12 b but rather the collection of observedechoes over a period of time. To collect such information, onetransducer must be trained on the school while others in the networkedsonar array 7 can be retasked in response to the controller 27, thenetworked sonar array to observe movement of a dynamic elements withinthe underwater environment 101. In this fashion, the focus of thenetworked array can be both on individual “trees” while maintaining aneye or rather an ear on the “forest.”

In a fourth non-limiting example, if the species of interest iscetacean, biological species even in schools will not be sufficientlyreflective as to be of interest. A whale has mass and volume thatpresents a large and reflective target to sonar. A school of fish suchas anchovy 99 d will not reflect sonar energy in the manner of whale.Whales have a relatively unvarying volume, well-defined margins, and agreater reflectivity than do a school of anchovy 99 d. Whales do notdart from one position within the underwater environment 101 to a secondposition. Where for the purposes of studying whale movement, thenetworked sonar array can identify the school of anchovies 99 d asanchovies, the most prudent deployment of resources may simply be tofilter out returns from the school of anchovies 99 d and to continue toallow each of the transducer assemblies 12 a, 12 b, and 12 c to continueto monitor their respective azimuths 126 a, 126 b, and 126 c. Using sucha non-limiting exemplary strategy allows maximum discernment of desiredtargets 99 within the underwater environment 101 by sacrificingknowledge of the exact movement of non-interesting targets within theunderwater environment 101.

While several strategies have been shown to describe the capabilities ofthe networked sonar array 7, the purpose of the description is not tolimit the networked sonar array to a number of taught responses totargets 99 within the underwater environment 101, but rather to indicatethe flexibility of the networked sonar array 7 in response to targets ofvarious interest within the underwater environment 101. Capabilities ofthe array 7 are the object of the teaching in this non-limitingdisclosure and strategies may vary in accord with the intended subjectof study. That the individual transducer assemblies 12 a, 12 b, and 12 care not required to observe fixed and unvaried azimuths 126 a, 126 b,and 126 c results from the independent training of the transducerassemblies 12 a, 12 b, and 12 c responsive to signals received from thecontroller 27.

Picket Configuration

One virtue of the networked sonar array is that the selection andtasking of transducer assemblies 12 may be according to the underwaterenvironment 101 to be observed. Where, for instance, the underwatertopography includes some of the features discussed in relation to FIGS.4 a and 4 b above, selecting and positioning transducer assemblies 12might well be accomplished through the selection of specializedtransducers.

By way of explanation, the non-limiting example of a volume of theunderwater environment 101 positioned between two piers might be a focusof study, especially, where as in this non-limiting example, pilings arespaced such that whales may only enter and leave the volume by passingbetween two extreme ends of the pair of piers.

Referring to FIG. 7, a first pier 112 a is parallel and spaced apartfrom a second pier 112 b and encompassing an underwater volume 101 a. Asecond view from within the underwater volume 101 a looking through themouth 101 b is presented in FIG. 8. At corresponding extreme ends of thepiers respective transducer assemblies 12 a and 12 b are trained toprovide a picket that covers a gateway or mouth 101 b to the underwatervolume 101 a.

Referring to FIGS. 7 and 8, the transducer assemblies 12 a and 12 b areselected to be wide-angle transducer assemblies, that is to saytransducer assemblies having wide-angle cones 123 a and 123 brespectively. Once mounted on the respective piers 112 a and 112 brespectively, the transducer assemblies 12 a and 12 b are trained toassure that the wide-angle cones 123 a and 123 b generally occlude themouth 101 b with minimal overlap. Frequencies for the transducers areselected to generate optimal responses from the environment (forinstance to penetrate silt of plankton known to be present). Theoperator may also select an optimal number of range bins within each ofthe cones 123 a and 123 b.

Placement of the transducer assemblies 12 a and 12 b in this “picket”formation completely filling the mouth 101 b of the volume 101 a,monitors movement into the volume without requiring that all of thevolume 101 a be constantly monitored. Thus, for example where anactivity such as spawning may occur within the area but such spawningneed not itself be observed, the perimeter picket yields all of theinformation of note. Where additional information is necessary, twotransducer assemblies 12 c and 12 d are mounted but not activated ortrained until the need arises or at such time when the controller 27(FIG. 6) generates orders to “exercise” the two-axis mounts 15 c, 15 d.

Additionally, the non-limiting deployment of the transducer assemblies12 a, 12 b, 12 c, and 12 d on their respective two-axis mounts 15 a, 15b, 15 c, and 15 d allows for redundancy in guarding the mouth 101 b.Alternately, the transducer assemblies 12 a and 12 b, can be placed inthe secondary job of tracing targets of interest by the controller 27(FIG. 6) while then using the transducer assemblies 12 c and 12 d toprovide the picket in a symmetric fashion to that illustrated in FIG. 8.

While the preferred embodiment of the invention has been illustrated anddescribed, as noted above, many changes can be made without departingfrom the spirit and scope of the invention. Accordingly, the scope ofthe invention is not limited by the disclosure of the preferredembodiment. Instead, the invention should be determined entirely byreference to the claims that follow.

The invention claimed is:
 1. A sonar transducer network for generatingbistatic images of an observed-seabed comprising: a controller togenerate a network time datum; a first transducer assembly including afirst transducer to generate a ping within the observed seabed at afirst ping time according to a first electrical signal; and a firsttransducer processor to receive a first electrical signal from the firsttransducer to generate the first transducer data, the first transducerdata including a first ping time datum; at least one second transducerassembly, spaced apart from the first transducer assembly, the secondtransducer assembly including: a second transducer to receive and toconvert the ping to a second electrical signal; and a second transducerprocessor to receive the second electrical signal from the secondtransducer to generate second transducer data, the second transducerdata including a second ping time datum; and a network bus tocommunicate first transducer data and second transducer data with thecontroller, the controller to timestamp the first transducer data toinclude the first ping time according to the network time datum and thesecond transducer data to include the second ping time according to thenetwork time datum.
 2. The sonar transducer network of claim 1, wherein:the network bus includes: a controller network interface communicativelyconnected to the controller; and a first addressable transducer networkinterface communicatively connected to the first transducer processor;at least one second addressable transducer interface communicativelyconnected to the at least one second transducer processor; and a networkconduit communicatively connected to each of the controller networkinterface; the first transducer network interface; and the at least onesecond transducer interface.
 3. The sonar transducer network of claim 2,wherein: the network interfaces include Ethernet interfaces; and thenetwork conduit includes an Ethernet cable.
 4. The sonar transducernetwork of claim 3, wherein: the network interfaces include fiber opticnetwork interfaces; and the network conduit is a fiber optic conduit. 5.The sonar transducer network of claim 1, wherein: the transducerprocessor includes an analog to digital converter in communication withthe transducer.
 6. The sonar transducer network of claim 1, wherein: thetransducer assembly includes environmental sensors to measure at leastone of environmental condition in the seabed proximate to the transducerselected from a group consisting of: temperature; salinity; and relativepressure.
 7. The sonar transducer network of claim 6, wherein: thetransducer processor is configured to normalize transducer data basedupon the at least one environmental condition.
 8. The sonar transducernetwork of claim 6, wherein: the transducer processor is configured tocommunicate the at least one environmental condition to the controller;and the controller normalizes the transit times based upon the at leastone environmental condition.
 9. The sonar transducer network of claim 1,wherein: the first transducer data includes: at least one transit timemeasured at a temporal moment; and a timestamp identifying the temporalmoment according to the first ping time.
 10. The sonar transducernetwork of claim 9, wherein: at least one of the transducer assembliesinclude: an at least two-axis mount affixed to the transducer; anazimuthal actuator configured to orient the transducer to an azimuthangle responsive to the transducer processor; and a depression actuatorconfigured to orient the transducer to a depression angle responsive tothe transducer processor.
 11. The sonar transducer network of claim 10,wherein: the transducer datum includes the azimuth angle and thedepression angle measured at the temporal moment.
 12. The sonartransducer network of claim 11, wherein: the controller includes: afirst buffer to store first transducer data according to temporalmoment, azimuth angle, and depression angle.
 13. The sonar transducernetwork of claim 12, wherein: the controller includes a second buffer tostore second transducer data according to temporal moment, azimuthangle, and depression angle; and the controller is further configured torefine the three-dimensioned model based upon second transducer data.14. The sonar transducer network of claim 13, wherein: the controller isconfigured to generate a three-dimensioned model of static elements ofthe seabed based upon first and second transducer data.
 15. The sonartransducer network of claim 14, wherein: the controller is furtherconfigured to suppress returns from targets based upon a positionrelative to the static elements of the three-dimensioned model.
 16. Amethod compiling ping data to generate a bistatic image of an observedseabed comprising: locating a plurality of benchmarks within the seabed;generating a network time datum; positioning a first transducer assemblysuitably to generate first transducer data to transmit an acoustic pingdirected at each of the plurality of benchmarks within the seabed toemanate from the first transducer assembly to include a first ping timedatum; positioning at least one second transducer assembly spaced apartfrom the first transducer assembly suitably to generate at least onesecond transducer data set from remotely sensing each returns from theacoustic ping directed at each of the plurality of benchmarks within theseabed at the at least one second transducer assembly; receiving thefirst and the at least one second transducer data at a controller, thecontroller to timestamp the first transducer data to include the firstping time according to the network time datum and the second transducerdata to include the second ping time according to the network timedatum; and storing first transducer data in a first buffer and the atleast one second transducer data in at least one second buffer accordingto a temporal moment and network time datum, azimuth angle, anddepression angle.
 17. The method of claim 16, further comprising:identifying data from each of the plurality of benchmarks in the firstbuffer as first benchmark data; identifying data from each of theplurality of benchmarks in the second buffer as second benchmark data;and correlating first benchmark data with second benchmark data togenerate a bistatic image of the benchmarks from the first transducerdata and the at least one second transducer data.
 18. The method ofclaim 17, further comprising: generating a digital elevation model ofseabed based upon the bistatic image, the first transducer data, and theat least one second transducer data.
 19. The method of claim 18, whereinthe generating on the digital elevation model includes: mapping a firstplurality of first point data, including a first azimuth angle, a firstdepression angle each measured at a first temporal moment, in the firsttransducer data relative to the first transducer assembly to develop afirst locus set; mapping a second plurality of second point data,including a second azimuth angle, a second depression angle, eachmeasured at a second temporal moment, relative to the second transducerassembly to develop a second locus set; and correlating the first pointdata to the second point data; and generating a correlated point data.20. The method of claim 19, further comprising: modeling the correlatedpoint data to generate a three-dimensioned model of the seabed.
 21. Themethod of claim 18, wherein: generating the digital elevation modelincludes: mapping the first plurality of first point data relative tothe first transducer assembly based upon a selected temporal moment; andmapping a second plurality of second point data relative to the secondtransducer to develop a second locus set based upon the temporal moment.22. The method of claim 21, wherein: generating the digital elevationmodel includes: selecting a temporal interval to include a substantiallycontinuous plurality of temporal moments.
 23. The method of claim 17,wherein the parallax image includes: static elements remainingsubstantially unchanged over time within a temporal interval; anddynamic elements varying over time within the temporal interval.
 24. Themethod of claim 23, further comprising: suppressing the static elementsin the parallax image to isolate dynamic elements in the parallax image.25. The method of claim 23, further comprising: grouping dynamicelements into targets according to variation within the temporalinterval.